PROJECT SUMMARY/ABSTRACT Evidence from experimental toxicology studies suggests that ultrafine particles (UFP) play a significant role in particulate matter (PM) respiratory toxicity because of their high potential to transport toxicants via a large number concentration and a large surface area per unit mass as compared with larger particles, including PM2.5. However, the theory that UFPs confer greater respiratory health risks than larger particles has not been validated in epidemiological settings. Experts identified the limitations of previous UFP studies, including the absence of data for concurrent exposures to other ambient pollutants, the error in characterizing exposure by using proxies such as fixed-site monitors or distance from roadways, and by exposure metrics used in those studies that did not provide information about how much PM would have been inhaled into the lungs. The proposed study intends to improve the method to assess UFPs exposures for respiratory health effect studies by addressing previous research gaps. The proposed Project Team's approach is to assess concurrent exposures to UFPs and other co-pollutants that can confound the UFP? lung function relationship for asthmatic adolescents, conduct a person-level assessment of spatio-temporal variability for each UFP and PM2.5, and apply inhaled PM doses that account for physiological process of PM intake and contact with the lungs to preliminarily determine the degree of lung function changes affected by UFP exposure from co-pollutants. We will apply novel exposure assessment approaches enabled by our innovative integration of wearable PM sensors, biometric sensors, and mobile data collection tool to produce high-quality exposure data sets that can delineate the effects of UFPs from other co-pollutants. This approach is essential because the traditional approach of using central fixed-site data or external exposure concentration data does not provide information about the amounts of contaminants that are inhaled by individuals, and it significantly underestimates the respiratory responses because of the exposures. This proposed effort will form the foundation of future work by informing of the study design and approaches to produce robust personal exposure data to multiple pollutants and by providing preliminary data regarding the distinct and joint effects of varying size fractions of PM and other pollutants on lung function by using innovative exposure metrics. Increased knowledge about the respiratory effects from UFPs will subsequently guide future environmental health policies, air pollution management strategies and control technologies, and interventions and clinical monitoring to reduce the burden of asthma.